1. Field of the Invention
The invention relates to an indicating device for showing the level of fluids in fluid containers using a transparent rod which is immersed in the fluid when the container is filled and the sensing end of which extending into the fluid is so formed that a beam of light running in the transparent rod undergoes total reflection at the sensing end when the sensing end is not in contact with fluid.
2. Description of the Prior Art
For the purposes of measuring the acid level in accumulators it is known for indicating devices to be screwed into position in place of the sealing plugs for the individual accumulator cells. These indicating devices consist of glass rods that are tapered conically at their end and are of a length corresponding to the minimum acid level in the accumulator. An indicating device of this kind works in the following way. When the acid level in the accumulator has dropped below the minimum level determined by the length of the rod and the cone on the rod is consequently no longer immersed, the light entering from outside undergoes total reflection at the conical end of the glass rod and the plane end of the glass rod appears as a bright spot. But when the accumulator is filled, the incident light is not reflected and the plane end of the glass rod appears dark.
Measurement of the level in a fluid container in the visual manner just named is only possible when the fluid container is directly accessible.
If such a transparent rod is to be used for example to measure the level of cleaning and sealing agent for protecting the rollers against toner in an electrographic high-speed printer, then it is necessary to provide a device which, when the cleaning and sealing agent falls below a minimum level, reliably signals this level to the operator.